Facebook is suspending political data analytics firm Cambridge Analytica, which worked for US President Donald Trump's 2016 election campaign, after finding data privacy policies had been violated.
The social media giant said in a statement that it suspended Cambridge Analytica and its parent group Strategic Communication Laboratories (SCL) after receiving reports they did not delete information about Facebook users that had been inappropriately shared.
Facebook did not mention the Trump campaign or any political campaigns in its statement. News site Vox reported it "might be a key Trump-Russia link".
"We will take legal action if necessary to hold them responsible and accountable for any unlawful behaviour," Facebook said, adding that it was continuing to investigate the claims.
Cambridge Analytica worked for the failed presidential campaign of US Senator Ted Cruz and then for the presidential campaign of Donald Trump.
Mr Trump's campaign hired Cambridge Analytica in June 2016 and paid it more than $6.2 million, according to Federal Election Commission records.
"We exploited Facebook to harvest millions of people's profiles," Cambridge Analytica whistleblower Christopher Wylie told the Observer, "and built models to exploit what we knew about them and target their inner demons. That was the basis that the entire company was built on."
The New York Times said interviews with a half-dozen former Cambridge Analytica employees and contractors, and a review of the firm's emails and documents, revealed it not only relied on the private Facebook data but still possesses most or all of it.
Brad Parscale, who ran Mr Trump's digital ad operation in 2016 and is his 2020 campaign manager, declined to comment on Friday, but in the past has said the campaign used voter data from a Republican-affiliated organisation rather than Cambridge Analytica.
The suspension means Cambridge Analytica and SCL cannot buy ads on the world's largest social media network or administer pages belonging to clients.
Facebook said it learned in 2015 that University of Cambridge professor Aleksandr Kogan lied to the company and violated its policies by sharing data that he acquired with a so-called "research app" that used Facebook's login system.
Facebook said that Mr Kogan gained access to profile and other information "in a legitimate way" but "he did not subsequently abide by our rules" when he passed the data to SCL/Cambridge Analytica and Christopher Wylie of Eunoia Technologies.
It cut ties to Mr Kogan's app when it learned of the violation in 2015, and asked for certification from Kogan and all parties he had given data to, that the information had been destroyed.
Although all certified that they had destroyed the data, Facebook said that it received reports in the past several days that "not all data was deleted", prompting the suspension announced on Friday.
Cambridge Analytica saidon Twitter it acted "legally and fairly", and was in touch with Facebook.